Method of making patterns



meh 5p 1946o H. J. PATTlsoN 2,395,195

METHOD OF MAKING PATTERNS Filed neg. 26, 1944 Patented Mar. 5, 1946UNITED STATES QFFICE BIETHOD F BIAKING PATTERNS Herbert J. Pattison,Grosse Pointe Park, Mich., assigner to Briggs Manufacturing Company,Detroit, Mich., a corporation of Michigan Application December 26, 1944,Serial No. 569,733

12 Claims.

This invention relates to the production of patterns for use inpreparing foundry molds utilized in the casting of metals, an object ofthe invention being to provide an improved method for reproducing orduplicating any existing master pattern, model or article so as toincrease the productive capacity of the foundry in casting articlescorresponding to the master pattern, model or article.

A further object of the invention is to provide an improved method forduplicating or reproducing a master pattern, article or model while atthe same time compensating for shrinkage so that the production castingsmade from the pattern duplications or reproductions will in no case beundersize and in fact may, if desired, be oversize to any predeterminedamount so as to allow for the removal of surface metal in finishingoperations.

Another object of the invention is to provide an improved method ofmaking patterns by reproducing an existing pattern, article or model andin such manner that the pattern reproduction will have sufficientoversize to compensate not only for shrinkage of the production castingbut also for any machining operations necessari7 for finishing thesurfaces of the casting.

Still another object of the invention is to provide a new and improvedmethod of making pat terns for use in preparing foundry molds, in whicha plaster or other impression is taken of the article to be reproducedand a pattern casting is made in this impression from a metal ormetallic allogghaving the property of growing in size after it Hascongealed and stood for a period of time. When the growth of the patterncasting has proceeded to an extent giving the desired oversize, aplaster or other impression is taken of the oversize pattern after whichthe iinal pattern is cast in this impression resulting in the productionof a pattern for use in preparing foundry molds having the requiredoversize to compensate forshrinkage of the production castings as wellas any needed iinishing of the surfaces thereof.

This application is a continuation in part oi' my application Serial No.510,131, led November 13, 1943.

Other objects of this invention will appear in the following descriptionand appended claims, reference being had to the accompanying drawingforming a part of this specication wherein like reference charactersdesignate corresponding parts in the several views.

Fig. 1 is a sectional view oi a flask containing a metal pattern orother article to be reproduced and illustrating the step of forming aplaster irnpression within the flask.

Fig. 2 is a sectional view of a iiask containing the plaster impressionand illustrating the step of forming a preliminary pattern castingwithin the flask.

Fig. 3 is a sectional view of a i'lask containing the preliminarypattern casting and illustrating the step of forming a plasterimpression within the ask. i

Fig. 4 is a sectional view of a liask containing the last mentionedplaster impression and illustrating the step of forming the finalpattern reproduction within the flask. l Before 'explaining in detailthe present invention it is to be understood-that the invention is notlimited in its application to the details of construction andarrangement of parts illustrated in the accompanying drawing, since theinvention is capable of other embodiments and of being practiced orcarried out in various Ways. Also it is to be understood that thephraseology or terminology employed herein is for the purpose ofdescription and not of limitation.

In the drawing there-is illustrated, by way of example, a suitablemasterv pattern, article of model ID to be reproduced or duplicated soas to provide a pattern which may be used in preparing a foundry mold.Inasmuch as any article, such for example as a iinished productioncasting or a master pattern or model, may be reproduced in accordancewith the present invention, it will be understood that the article l0may be of any type or category in which backdraft is eliminated so as topermit an impression to be made of the article utilizing suitablemoldable material for this purpose, such as plaster or calcined gypsum.In carrying out the first step of the method the pattern or article i0to be reproduced or duplicated, which may be of metal, wood or othersuitable material, is placed within the bottom of a iiask H supportedupon a table or other suitable base. Where plaster is used to make theimpression of the exposed side of the article I0, the plaster orcalcined gypsum is mixed with water to produce a flowable material whichis poured into the ask and allowed to set, thus providing a solid moldimpression l2. The mold impression is then removed from the flask andallowed to dry.

In carrying out the second step of the invention illustrated in Fig. 2,the plaster impression !2 is reversed and placed upon a supporting plateI3 within a suitable fiask i4 held in position upon the supportingplateby means of locating dowel pins l5. Mounted upon the upper edge ofthe flask le is a cover plate or closure member I6 notched or groovedalong its edges at Il to receive the upper edges of the flask andposition the cover plate I6 properly with respectlthereto. This plate isprovided with pairs of shrink-control depending ribs i8 extending lasuitable distance within the ask and is also provided at one sidethereof with an opening or hole I9 through which molten metal may; bepoured into the space between thelcover plateu and the plasterimpression l2 to provide a cast impression 20 of the upper side oftheplaster,

The ribs I8 Vattheunclerside:offV the cover plate I6 are boundedbya'groove-or` channel |6a extending around the four sides, of the coverplate providing in the casting 2Q' This marginal rib Y,

member I 2.

a continuous marginal rib 2l. is joined by longitudinal ribs and alsobyacentral transverse'rib 22 connecting'two opposite sides ofthe ribl2l. The depending-ribs IS serve to quickly chill the metal within thecavityl by rapidly conducting the heat from the molten metal away,thereby eliminating shrinkage or other defects on the working surfacesof the pattern casting. The ribs '2l and 22 provide ameans by which thecasting 20, when inverted, may be supported evenly upon a base inorderto carry out the next step of the method.

The metal employed in forming the/prelimi-v nary pattern casting '20 ispreferably alow melting alloy which has very low shrinkage propertieswhen the'metal in molten state congeals o1' solidifies and which' aftersolidiication will grow in size when allowedtostand for a predeterminedperiod of time. One low melting point alloy. which may be usedfor thepurposes of the` present invention, is an alloy of 58% bismuth and 42%lead known commercially as Cerrobase having a melting point ofapproximately 285 F. A castingY formed from this alloy. such as thepattern casting- 20, will shrink to little or no extent when the moltenmetal congeals and solidies. However, after the casting has beenremovedfrom the ask and'allowed to stand for a number of hours; thecasting will grow in size; This growthis uniform in alldirections andthe amount of oversize may be predetermined by the length of time whichthe pattern casting 20 is allowed to stand. For example, the casting 2Dafter removal from the ask I4k may be permitted to erow'to apredetermined amount such as .005 per inch.

When the pattern casting 20 has reached the proper oversize, it'isinverted andmounted within av iiask 23 and awet plaster mix is pouredinto the ask to produce a mold impression 21S. After the plastermaterialwithin the ask has set sufciently it is removed therefrom and'thoroughlydried. Thus'. it will be-seen that inthe stepof the method illustratedinFig. 3 a plaster impression 24 is made of the oversize pattern casting2li and, hence, the mold impression 2li' As in'. thecase ofthe closureplatel 6, the closuremem ber 28 is so constructed as to control theshrink- :the member 28 is formed with a marginal groove or channel 28aextending around the four sides thereof and is also provided withcross-channels or grooves forming intervening ribs 3K) of substantialdepth and width. The closure or cover plate 23 is also provided with a.pouring aperture 3l VV.through which molten metal, such as brass, is

poured to produce the final pattern casting 32. This castingywill beprovided with a continuous marginal rib 33 extending around the foursides thereof and cross-ribs 3ft.

Assumingvthatthe preliminary pattern casting 2i! 'is allowed to grow toan oversize such, for example as .005 per inch, and also assuming thatthe allowance necessary for the shrinkage of the metal forming thecastingf32 andthe shrinkage of the iinal production casting is in eachinstance .002 per inch, it will be seen that the mold impression 24taken of the oversize pattern casting 29 will in effect have a doubleshrinkage value of .004 per inch plus an additional amount'of oversizeof .001 perlinch. Having assumed, for purposes of illustration, that themetal forming the final pattern casting 32 will shrink .002 per inch,then it will be apparent that-this'pattern will be oversize an amountequal 'to .003 per inch. Thus, a production mold of plaster or othermolda-ble material formed from the nal pattern 32 will provide acastingv cavity which' will be'oversize an amount equal'to .003 perinch. This oversize will not only allow for the shrinkage of theproduction casting, assumed lfor the purposes of illustration to be atthe rate of .002 per inch, but in addition will allow an amount of metalequal to .001 per inch to be removed from the surface of the productioncasting in finishing operations. After this amount of metal hasbeenremoved in the nishing operations the nal production casting will besubstantiallyz the-exact sizeof Ythe master pattern, model or articleI!) employed in making the initial mold impression l2.

Thus. it will beseen that by preparing the intermediate vpattern casting2U from a metal alloy having the property of growing or increasing insizeafter standing, it is possible to'produce a final production pattern32 having sufficient oversize to allow for shrinkage ofthe productioncasting as well as 4the removal of metal in argv machining f operationsyneeded to finish the surfaces'thereof.

The allowable growth of the pattern casting 28 may be controlled withinexact limit-s in order` to meet requirements and when the predeterminedoversize has'been attained the plaster impression 24 is made after whichthe nal pattern 32 is poured in the flask 26 as previously described.

The example given above is especially applicable to the production of afoundry pattern from an article, such as a production casting, whichcannot be practicably used as a pattern in the preparation of foundrymolds since such casting has no oversize allowance for shinkage of metalcast in such molds. In the event the article l0 is a foundry pattern,which it is desired to duplicate, and which pattern has an oversizeallowance for single shrinkage;v then the amount of growth ofv thepattern casting 2B need not be as great as vwould be necessary in theexample given above where itis necessary to provide for doubleshrinkage. In such instance, assuming the article lil is a productionpattern having a single shrinkage allowance, the pattern 20 willl beallowed to grow an amount greater in size than the size of the patternHl sufficient to offset the shrinkage of the metal used in casting thefinal pattern 32 which will then be a duplication in size of the patternIii. Additional growth to com pensate for finishing operations may ofcourse be permitted as in the example given above.

I claim:

1. The method of producing a metal pattern, including the steps ofmaking a mold impression of an article to be reproduced, casting apattern in said impression with a metal having the property of growingin size when allowed to stand, allowing said pattern casting to grow toa predetermined oversize, making a mold impression of said oversizepattern casting, and casting in metal a pattern from said last namedmold impression.

2. The method of producing a metal pattern, including the steps ofmaking a plaster mold impression of an article to be reproduced, castinga pattern in said impression with a metal alloy having the property ofgrowing in size when allowed to stand, allowing said pattern casting togrow to a predetermined oversize, making a plaster mold impression ofsaid oversize pattern casting, and casting in metal a pattern from saidlast named mold impression.

3. The method of producing a metal pattern, including the steps ofmaking a mold impression of an article to be reproduced, casting apattern in said impression with a low melting metal alloy having theproperty of growing in size when allowed to stand, allowing said patterncasting to grow to a predetermined oversize, making a mold impression ofsaid oversize pattern casting, and castingr in metal a pattern from saidlast named mold impression.

4. The method of producing a metal pattern, including the steps offorming from moldable material a mold impression of an article casting apattern in said impression from a metallic alloy having growth producingproperties. allowing said pattern casting after cooling to stand for apredetermined period of time so as to grow uniformly to a size greaterthan said articlethen making a mold impression from said pattern castingand casting a metal pattern in said last mold impression.

5. The method of producing a metal pattern, including the steps offorming from moldable material a mold impression of an article. castingra Dai-.tem in said impression from a metallic alloy having growthproducing properties and adapted to melt at a temperature below 300 F..allowing said pattern casting after cooling to stand for a predeterminedperiod of time so as to grow uniformly to a size greater than saidarticle, then making a roold impression from said pattern cast.. ing andcasting a metal pattern in said last mold impression.

6. The method oi producing a metal pattern. including the steps offorming from moldable plaster or gypsum material a mold impression of anarticle, casting a pattern in said impression from a metallic alloyhaving growth producing properties, allowing said pattern casting aftercooling to stand for a predetermined period of time so as to growuniformly to a size greater than said article, then making a plastermold impression from said pattern casting and casting a metal pattern insaid last mold impression.

7. The method of producing a metal pattern.

including 'the steps of positioningan article'in a flask, pouring a wetplaster mix into the flask to produce a mold impression of said article,drying and positioning said mold impression in a ask, pouring moltenmetal into said flask to produce a pattern casting from said moldimpression. said metal having the property of growing in size whenallowed to stand after a casting operation, allowing said patterncasting to stand for a predetermined period of time so as to increase apredetermined amount in size uniformly throughout all dimensionsthereof, positioning the oversize pattern casting in a ilask, pouring awet plaster mix into the flask to produce a mold impression of saidoversize pattern casting, drying and then positioning said last moldimpression in a fiask and casting a metal pattern in said last mentionedilask of said last mold impression.

8. The method of producing a metal pattern, including the steps ofpositioning an article in a flask, pouring a wet plaster mix into theflask to produce a mold impression of said article, drying andpositioning said mold impression in a flask, pouring molten metal intosaid ask to produce a pattern casting from said mold impression, saidmetal comprising a low melting alloy having the property of growing insize when allowed to stand after a casting operation, allowing saidpattern casting to stand for a predetermined period of time so as toincrease a predetermined amountl in size uniformly throughout alldimensions thereof up to .005 per inch or less, positioning the oversizepattern casting in a ask, pouring a wet plaster mix into the iiask toproduce a mold im pression of said oversize pattern casting, drying andthen positioning said last mold impression in a flask, and casting ametal pattern in said last mentioned flask of said last mold'impression.

9. The method of producing a metal pattern, including the steps ofmaking a mold impression of an article to he reproduced, casting apattern in said impression with a metal having the property of growingor increasing uniformly in size when allowed to stand after a castingoperation, allowing said pattern casting to grow an oversize amountnecessary to allow for double shrinkage, making a mold impression ofsaid oversize pat tern casting, and casting a pattern in said last moldimpression which after shrinkage and cooling has an oversize suflicientto allow for the shrinkage of a production casting made in a mold formedfrom said last named pattern.

10. The method of producing a metal pattern, including the steps ofmaking a mold impression of an article to be reproduced, casting apattern in said impression with a metal having the prop erty of growingor increasing uniformly in size when allowed to stand after a castingoperation, allowing said pattern casting to grow an oversize amountnecessary to allow for the shrinkage of a metal cast in a mold preparedfrom said pattern casting, making a mold impression of said oversizepattern casting, and casting a metal pattern in said last moldimpression.

11. The method of producing a metal pattern, including the steps ofmaking a plaster mold impression of an article to be reproduced, castinga pattern in said impression with a low melting metal alloy having theproperty of growing or increasing uniformly in size when allowed tostand after a casting operation, allowing said pattern casting to growan oversize amount necessary to allow for double shrinkage, making aplaster mold impression of said oversize pattern casting, and casting apattern in said last mold impression which; alter shrinkage; and coolinghas an f over-- sizesuiicientzto -allowffon the kshrinkage ofia,production; castingmadepina mold formed from said 1ast1namedfpattern 12.yThey method; ofg producing ametalY pattern, including: the stepslofmaking; a plaster. mold impression; of; an article, to be reproduced.castingV agpatterninsaid impression withvalow melting metalalloyhavingthe yproperty yof growing lor increasing: uniformlyv in vsize whenallowed to stand after .a castingv operation.` allowingy said patterncasting tovgrow` an oversize amount vnecessary to allow for theshrinkage vof a metal cast in a` mold prepared from said patterncasting,. making a plaster mold impression ofv said oversize patterncasting, and,4 casting. a metal pattern inrsaid last mold impression.

HERBERT J. PATTISON.

